Work machines, including on-highway vehicles, may have a main power source for moving the work machine. The main power source may also be used to power electrical accessories including, for example, an air conditioning system, a heater, lights, and various other accessories. The main power source may be an engine such as a diesel engine, a gasoline engine, a natural gas engine, or any other type of engine that may be used for powering a work machine.
The main power source must be running to power the electrical accessories of the work machine with the main power source. This may lead to idling the main power source for extended periods. For example, while parked, a machine operator may have to idle the main power source to power the air conditioner, a TV, or other appliances. Such extended periods of idling can result in high fuel consumption, increased emissions, and increased wear of the main power source.
U.S. Pat. No. 5,528,901 (the '901 patent), issued to Willis on Jun. 25, 1996, describes the use of an auxiliary power unit (APU) to meet the power demands of the work machine without necessarily idling the main power source for extended periods. The APU is a secondary engine that produces power that may be used to provide for the accessory electrical loads of the work machine. The APU may allow the main power source of the work machine to be turned off when the APU power generating capacity is sufficient to meet the demands of the accessory electrical loads of the work machine.
The APU described in the '901 patent may also aid in cold starting situations. Specifically, the APU may be used to pass oil, warmed by the APU, to or through the main power source prior to starting the main power source. The warm oil circulating through the main power source increases main power source temperature, which improves startability.
Although the APU of the '901 patent may alleviate some of the difficulty associated with cold starting and may provide additional power for the work machine, the separate main engine and APU lubrication systems of the '901 patent are problematic. For example, separate lubrication systems may require separate maintenance activities. As a result, the operator may be required to shut down the work machine a greater number of times in order to maintain the work machine. Shutting down in this way may reduce machine efficiency and increase operating costs. Further, separate fluid level inspections may have to be performed for the APU and the main engine. These added maintenance activities and inspections may also increase the opportunity for errors. In addition, the location of the APU within the work machine may increase the difficulty of the maintenance and inspection activities.
The present invention is directed to overcoming one or more of the problems set forth above.